Acne, the Skin Microbiome, and Antibiotic Treatment

Overview

This review, published in the American Journal of Clinical Dermatology in 2019, examines how acne vulgaris, the skin microbiome and antibiotic treatment are connected. Acne is a common chronic disorder of the hair follicle and sebaceous gland. Four processes are thought to drive it: excess sebum production, abnormal growth and shedding of follicular keratinocytes, bacterial colonization and the host inflammatory response. Because antibiotics have been a mainstay of acne treatment for decades, the authors look at what this long-standing practice means for skin microbes and for antibiotic resistance.

Microbes involved in acne

Cutibacterium acnes (formerly Propionibacterium acnes) is the dominant species in the pilosebaceous unit. It is thought to contribute to acne by increasing sebum secretion, promoting comedone formation and triggering inflammation through innate immune receptors, the complement system and the inflammasome. At the same time it is an important commensal that helps keep skin pH low and limits colonization by pathogens. Genome studies show that its effect depends on the strain: some lineages are strongly associated with acne and carry extra virulence genes, while others are linked to healthy skin. Staphylococcus epidermidis may restrain C. acnes, and the yeast Malassezia has been suggested as a contributor, particularly in acne that does not respond to treatment.

Antibiotics and resistance

Macrolides, clindamycin and tetracyclines are the most widely prescribed antibiotics for acne. Resistance of C. acnes to macrolides and clindamycin has risen in many parts of the world, and resistance to one often comes with resistance to the other. Resistant strains can persist on the skin after treatment and reduce the effect of later courses. Tetracyclines remain active against most isolates, but resistance to them is also growing. Antibiotic use affects other skin bacteria as well, selecting resistant staphylococci at both treated and untreated sites.

Implications for practice

Antibiotic monotherapy, whether topical or oral, is discouraged. Topical antibiotics should be combined with benzoyl peroxide or a topical retinoid, and oral antibiotics should be used together with topical therapy for limited courses rather than long term. Previous exposure to an antibiotic class should inform the choice of drug, and hormonal options may be an alternative for some women. The authors call for antibiotic selection guided by strain type and susceptibility, and point to vaccines and microbiome-based therapies as possible future alternatives.